The invention relates to a system comprising a compressor and a consumer, which are coupled to a drive train and extract energy therefrom. The invention further relates to a pump, which has at least one pump chamber which generates pumping power during a pumping operation.
In motor vehicles, systems comprising compressors are frequently used. Thus compressors are used, for example, for supplying compressed air for brakes, pneumatic suspension, gear units, etc. Generally, the compressor is driven by an internal combustion engine of the motor vehicle via a drive train, which may be disconnected by means of a clutch device for relieving the internal combustion engine, if the boundary conditions permit this.
Moreover, modern motor vehicles are generally provided with power-assisted steering, also known as a servo-assisted steering, which substantially consists of a power steering pump or hydraulic pump, such as for example an oil pump, and a hydraulic circuit, via which the hydraulic pump supplies a hydraulic pressure to the power-assisted steering coupled to a steering linkage. As a result, an auxiliary force is produced which is applied by means of a suitable mechanical means to the steering wheel in an assisting manner. The hydraulic pump is frequently driven indirectly, i.e. indirectly by the drive train of the internal combustion engine. For example, the compressor is arranged in the drive train between the internal combustion engine and the hydraulic pump, the compressor in turn driving the hydraulic pump as a consumer.
Generally, compressors exhibit an uneven characteristic of the drive torque required for compressor operation and/or of the driving power required for compressor operation, the drive torque and/or the driving power being provided by the internal combustion engine. For example, when the compressor performs a compression cycle and/or a compression stroke, the drive torque required for compressor operation is particularly high in comparison with an expansion cycle and/or expansion stroke. This may be observed primarily with piston compressors having at least one cylinder. The drive torque required in the compression cycle for compressor operation, and/or the driving power required therefor, increases with the progression of the piston in the direction of the top dead center in the cylinder and, in a region in the vicinity of the top dead center, finally reaches a peak value, hereinafter denoted the torque peak or power peak. As a result of the torque peak, retrospective effects are produced on the internal combustion engine, for example on the gear train of the internal combustion engine.
Similarly, disruptions to the precise running of the cam shaft may be caused. Thus a constant and/or uniform characteristic is desired of the torque and/or power which the internal combustion engine produces.
Moreover, an increased drive torque and/or an increased driving power of the internal combustion engine is required when, in addition to the compressor, a power steering pump or hydraulic pump has to be driven which is located in the same drive train of the compressor. Similarly, the clutch device provided in the drive train of the internal combustion engine has to be designed according to the maximum transmitted drive torque and/or the maximum supplied driving power of the internal combustion engine.
It is, therefore, the object of the present invention to improve the generic system further with regard to the loading of the components arranged in the drive train.
The system according to the invention has a compressor and a consumer, which are coupled to a drive train and extract energy therefrom. The consumer is suitable for varying an absorption of a power provided thereto by the drive train depending on a power which is required for compressor operation and supplied from the drive train to the compressor. The dependence of the power absorption of the consumer on the power required for compressor operation, which is supplied to the compressor, is advantageous insofar that a power provided in the drive train, such as for example a time characteristic of a total power, may be positively influenced by suitable variation of the power absorption of the consumer.
Advantageous embodiments and developments of the invention are described herein.
In a preferred embodiment of the system according to the invention, it is provided that the consumer is suitable for varying its absorption of the power provided thereto, such that a characteristic of the total power consisting of the power required for compressor operation and the power absorbed by the consumer is substantially constant. This development is particularly advantageous as the compressor during compressor operation, in principle, has a very uneven characteristic of the driving power required for compressor operation and/or of the drive torque required for compressor operation. By corresponding variation of the power absorption of the consumer, said uneven characteristic is compensated as a whole. This is based, therefore, on the fact that the total torque provided in the drive train and/or the total power provided in the drive train is a superposition of the drive torque and/or driving power required for compressor operation and the torque and/or power absorbed by the consumer. Thus possible retrospective effects due to torque fluctuations or torque peaks on the drive train, which for example is branched off from an internal combustion engine, are avoided.
Moreover, the system according to the invention may be developed by the consumer being suitable for reducing its absorption of the power provided thereto, when a characteristic of the power required for compressor operation rises above a predetermined threshold value, or reaches a maximum power range. By setting the threshold value, it is prevented that the total torque characteristic and/or the total power characteristic in the drive train exceeds a maximum permissible value, at the same time a power peak and/or a torque peak in the drive train being avoided. The level of the threshold value is thus established such that, advantageously, retrospective effects on the drive train, for example on an internal combustion engine located in the drive train, are substantially prevented.
Moreover, the system according to the invention may be developed such that the power required for compressor operation in a compression cycle or a compression stroke exceeds the threshold value or reaches its maximum power. In particular, during a compression cycle, a very high torque and/or a very high driving power may be required for driving the compressor. The high drive torque which reaches a very high torque peak shortly before reaching the top dead center, in piston compressors, may be compensated as mentioned above. Thus, it is particularly advantageous to reduce the power absorption of the consumer precisely when the compressor performs its compression cycle, in particular shortly before reaching the top dead center, in order to ensure a uniform total power characteristic and/or total torque characteristic in the drive train.
The system according to the invention may furthermore be designed such that the consumer includes a pump, in particular a power steering pump or a hydraulic pump, which is suitable for carrying out an operation providing a pumping power, in which the power provided is absorbed, and an operation producing no pumping power or reduced pumping power depending on the operating conditions of the compressor, in which no absorption or reduced absorption of the power provided takes place. By means of this development, the pump located in the drive train, which generally has a uniform torque characteristic and/or power characteristic, is adapted to the characteristic of the power required and supplied for compressor operation, in order to achieve the above-mentioned constant characteristic of the total power.
In a preferred embodiment, the system according to the invention is designed such that the pump is a displacement pump, in particular a vane pump or a piston pump, in which at least one pump chamber is formed, providing no pumping power or reduced pumping power depending on the operating conditions of the compressor, by which in a pumping operation no absorption or reduced absorption of the power provided takes place, the pump further including at least one pump chamber providing a pumping power, by which in a pumping operation the power provided is absorbed. By this design of the pump, it is possible that by structural measures on the pump chambers the abovementioned variable operations may be performed. Thus the vane pump may have more than 6 pump chambers, of which one portion of the chambers is able to be transferred into a “non pumping” state, in order to reduce the power absorption during operation of this pump chamber and thus to achieve the above-mentioned compensation of the peak torque. This may, for example take place by an enlarged chamber volume in a vane pump, which for example in the case of the vane pump may be increased by redesigning the rotor, i.e. using a rotor which is flattened on one side relative to the rotor longitudinal axis, which on the flattened side partially forms the pump chamber providing no pumping power. Similarly, however, a design of a pump chamber providing a reduced pumping power is also contemplated, the pumping power capacity thereof being made dependent on various factors. Moreover, other measures are also contemplated which prevent an operation of the corresponding chamber(s) producing pumping power. Thus, for example, with piston pumps having a plurality of cylinders, in particular with a swash plate piston pump, the elimination of one or more pistons may prevent any pumping power for this corresponding chamber.
The system according to the invention may, moreover, be developed such that the compressor is driven by a drive train of an internal combustion engine and the consumer is driven by a drive train of the compressor, optionally a clutch device being arranged in the drive train of the internal combustion engine. This development proves particularly advantageous, as the internal combustion engine provides the compressor with a constant characteristic of the drive torque and/or a constant characteristic of the driving power, without an increase in the drive torque occurring as a result of the compressor cycle, whereby problems in the gear train of the engine and disruptions to the precise running of the cam shaft due to the compensation of the torque peak may be avoided. Similarly, the system according to the invention permits, with the use of a clutch device such as an idling clutch, the reduction in size thereof and thus the lowering of the costs arising therefrom, as the clutch device is designed for the maximum drive torque of the compressor and/or the torque peak. It is noteworthy that the arrangement mentioned here corresponds to an arrangement of the engine, compressor and consumer in series. However, equally a parallel arrangement of the compressor and consumer or other arrangements are contemplated provided the compressor and consumer are coupled to the same drive train.
The pump according to the invention is based on the prior art such that it further includes at least one pump chamber, which during the pumping operation provides no pumping power or a reduced pumping power. Generally, the advantages cited in connection with the power steering pump and/or hydraulic pump apply thereto.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.